Address initial comments

src/core/ext/filters/http/client/http_client_filter.cc

@@ -107,7 +107,7 @@ static grpc_error* client_filter_incoming_metadata(grpc_call_element* elem,
      * https://github.com/grpc/grpc/blob/master/doc/http-grpc-status-mapping.md.
      */
     if (b->idx.named.grpc_status != nullptr ||
-        grpc_mdelem_eq_static(b->idx.named.status->md,
+        grpc_mdelem_static_value_eq(b->idx.named.status->md,
                                     GRPC_MDELEM_STATUS_200)) {
       grpc_metadata_batch_remove(b, b->idx.named.status);
     } else {
@@ -141,7 +141,7 @@ static grpc_error* client_filter_incoming_metadata(grpc_call_element* elem,
   }
 
   if (b->idx.named.content_type != nullptr) {
-    if (!grpc_mdelem_eq_static(
+    if (!grpc_mdelem_static_value_eq(
             b->idx.named.content_type->md,
             GRPC_MDELEM_CONTENT_TYPE_APPLICATION_SLASH_GRPC)) {
       if (grpc_slice_buf_start_eq(GRPC_MDVALUE(b->idx.named.content_type->md),

src/core/ext/filters/http/server/http_server_filter.cc

@@ -131,23 +131,23 @@ static grpc_error* hs_filter_incoming_metadata(grpc_call_element* elem,
   static const char* error_name = "Failed processing incoming headers";
 
   if (b->idx.named.method != nullptr) {
-    if (grpc_mdelem_eq_static(b->idx.named.method->md,
-                              GRPC_MDELEM_METHOD_GET)) {
-      *calld->recv_initial_metadata_flags |=
-          GRPC_INITIAL_METADATA_CACHEABLE_REQUEST;
-      *calld->recv_initial_metadata_flags &=
-          ~GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST;
-    } else if (grpc_mdelem_eq_static(b->idx.named.method->md,
+    if (grpc_mdelem_static_value_eq(b->idx.named.method->md,
                                     GRPC_MDELEM_METHOD_POST)) {
       *calld->recv_initial_metadata_flags &=
           ~(GRPC_INITIAL_METADATA_CACHEABLE_REQUEST |
             GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST);
-    } else if (grpc_mdelem_eq_static(b->idx.named.method->md,
+    } else if (grpc_mdelem_static_value_eq(b->idx.named.method->md,
                                            GRPC_MDELEM_METHOD_PUT)) {
       *calld->recv_initial_metadata_flags &=
           ~GRPC_INITIAL_METADATA_CACHEABLE_REQUEST;
       *calld->recv_initial_metadata_flags |=
           GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST;
+    } else if (grpc_mdelem_static_value_eq(b->idx.named.method->md,
+                                           GRPC_MDELEM_METHOD_GET)) {
+      *calld->recv_initial_metadata_flags |=
+          GRPC_INITIAL_METADATA_CACHEABLE_REQUEST;
+      *calld->recv_initial_metadata_flags &=
+          ~GRPC_INITIAL_METADATA_IDEMPOTENT_REQUEST;
     } else {
       hs_add_error(error_name, &error,
                    grpc_attach_md_to_error(
@@ -164,7 +164,8 @@ static grpc_error* hs_filter_incoming_metadata(grpc_call_element* elem,
   }
 
   if (b->idx.named.te != nullptr) {
-    if (!grpc_mdelem_eq_static(b->idx.named.te->md, GRPC_MDELEM_TE_TRAILERS)) {
+    if (!grpc_mdelem_static_value_eq(b->idx.named.te->md,
+                                     GRPC_MDELEM_TE_TRAILERS)) {
       hs_add_error(error_name, &error,
                    grpc_attach_md_to_error(
                        GRPC_ERROR_CREATE_FROM_STATIC_STRING("Bad header"),
@@ -179,11 +180,11 @@ static grpc_error* hs_filter_incoming_metadata(grpc_call_element* elem,
   }
 
   if (b->idx.named.scheme != nullptr) {
-    if (!grpc_mdelem_eq_static(b->idx.named.scheme->md,
+    if (!grpc_mdelem_static_value_eq(b->idx.named.scheme->md,
                                      GRPC_MDELEM_SCHEME_HTTP) &&
-        !grpc_mdelem_eq_static(b->idx.named.scheme->md,
+        !grpc_mdelem_static_value_eq(b->idx.named.scheme->md,
                                      GRPC_MDELEM_SCHEME_HTTPS) &&
-        !grpc_mdelem_eq_static(b->idx.named.scheme->md,
+        !grpc_mdelem_static_value_eq(b->idx.named.scheme->md,
                                      GRPC_MDELEM_SCHEME_GRPC)) {
       hs_add_error(error_name, &error,
                    grpc_attach_md_to_error(
@@ -200,7 +201,7 @@ static grpc_error* hs_filter_incoming_metadata(grpc_call_element* elem,
   }
 
   if (b->idx.named.content_type != nullptr) {
-    if (!grpc_mdelem_eq_static(
+    if (!grpc_mdelem_static_value_eq(
             b->idx.named.content_type->md,
             GRPC_MDELEM_CONTENT_TYPE_APPLICATION_SLASH_GRPC)) {
       if (grpc_slice_buf_start_eq(GRPC_MDVALUE(b->idx.named.content_type->md),

src/core/ext/transport/chttp2/transport/chttp2_transport.cc

@@ -1281,7 +1281,7 @@ void grpc_chttp2_complete_closure_step(grpc_chttp2_transport* t,
 
 static bool contains_non_ok_status(grpc_metadata_batch* batch) {
   if (batch->idx.named.grpc_status != nullptr) {
-    return !grpc_mdelem_eq_static(batch->idx.named.grpc_status->md,
+    return !grpc_mdelem_static_value_eq(batch->idx.named.grpc_status->md,
                                         GRPC_MDELEM_GRPC_STATUS_0);
   }
   return false;

src/core/lib/transport/metadata.h

@@ -124,7 +124,18 @@ grpc_mdelem grpc_mdelem_create(
     const grpc_slice& key, const grpc_slice& value,
     grpc_mdelem_data* compatible_external_backing_store);
 
+#define GRPC_MDKEY(md) (GRPC_MDELEM_DATA(md)->key)
+#define GRPC_MDVALUE(md) (GRPC_MDELEM_DATA(md)->value)
+
 bool grpc_mdelem_eq(grpc_mdelem a, grpc_mdelem b);
+/* Often we compare metadata where we know a-priori that the second parameter is
+ * static, and that the keys match. This most commonly happens when processing
+ * metadata batch callouts in initial/trailing filters. In this case, fastpath
+ * grpc_mdelem_eq and remove unnecessary checks. */
+inline bool grpc_mdelem_static_value_eq(grpc_mdelem a, grpc_mdelem b_static) {
+  if (a.payload == b_static.payload) return true;
+  return grpc_slice_eq(GRPC_MDVALUE(a), GRPC_MDVALUE(b_static));
+}
 
 /* Mutator and accessor for grpc_mdelem user data. The destructor function
    is used as a type tag and is checked during user_data fetch. */
@@ -144,9 +155,6 @@ grpc_mdelem grpc_mdelem_ref(grpc_mdelem md);
 void grpc_mdelem_unref(grpc_mdelem md);
 #endif
 
-#define GRPC_MDKEY(md) (GRPC_MDELEM_DATA(md)->key)
-#define GRPC_MDVALUE(md) (GRPC_MDELEM_DATA(md)->value)
-
 #define GRPC_MDNULL GRPC_MAKE_MDELEM(NULL, GRPC_MDELEM_STORAGE_EXTERNAL)
 #define GRPC_MDISNULL(md) (GRPC_MDELEM_DATA(md) == NULL)
 
@@ -160,9 +168,4 @@ void grpc_mdelem_unref(grpc_mdelem md);
 void grpc_mdctx_global_init(void);
 void grpc_mdctx_global_shutdown();
 
-inline bool grpc_mdelem_eq_static(grpc_mdelem a_static, grpc_mdelem b_static) {
-  if (a_static.payload == b_static.payload) return true;
-  return grpc_slice_eq(GRPC_MDVALUE(a_static), GRPC_MDVALUE(b_static));
-}
-
 #endif /* GRPC_CORE_LIB_TRANSPORT_METADATA_H */

src/core/lib/transport/status_metadata.cc

@@ -31,13 +31,13 @@
 static void destroy_status(void* ignored) {}
 
 grpc_status_code grpc_get_status_code_from_metadata(grpc_mdelem md) {
-  if (grpc_mdelem_eq_static(md, GRPC_MDELEM_GRPC_STATUS_0)) {
+  if (grpc_mdelem_static_value_eq(md, GRPC_MDELEM_GRPC_STATUS_0)) {
     return GRPC_STATUS_OK;
   }
-  if (grpc_mdelem_eq_static(md, GRPC_MDELEM_GRPC_STATUS_1)) {
+  if (grpc_mdelem_static_value_eq(md, GRPC_MDELEM_GRPC_STATUS_1)) {
     return GRPC_STATUS_CANCELLED;
   }
-  if (grpc_mdelem_eq_static(md, GRPC_MDELEM_GRPC_STATUS_2)) {
+  if (grpc_mdelem_static_value_eq(md, GRPC_MDELEM_GRPC_STATUS_2)) {
     return GRPC_STATUS_UNKNOWN;
   }
   void* user_data = grpc_mdelem_get_user_data(md, destroy_status);